JP4429939B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that forms an image on a supplied sheet, and more particularly to control of a driving speed of an intermediate conveyance roller that conveys a sheet to a registration roller.

  An intermediate conveyance roller that conveys a sheet to a registration roller (a roller that performs skew correction and timing adjustment of the conveyed sheet) in the image forming apparatus conveys the sheet together with the registration roller when forming an image on the sheet, and also feeds a sheet. And a sheet that is formed on the first side and conveyed to form an image on the second side (to perform double-sided printing).

  In the intermediate conveyance roller having the above-described role, it is preferable that the sheet conveyance speed is synchronized with a conveyance roller or a registration roller which is a partner to which the sheet is transferred. The sheet conveyance speed that the intermediate conveyance roller should synchronize is as follows: sheet feeding speed (speed when conveying the sheet supplied from the cassette to the registration roller), process speed (sheet conveyance speed during toner image transfer) , And ADU speed (conveying speed of a sheet re-feeded to form an image on the second surface).

  As a technique for realizing a plurality of types of sheet conveyance speeds in the intermediate conveyance roller, a pulse motor is frequently used to drive the conveyance roller that conveys the sheet in the apparatus, or a plurality of clutch mechanisms are used. However, these methods have a problem of hindering cost reduction.

  In addition, the configuration in which the intermediate conveyance roller is driven by the clutch has only realized two types of sheet conveyance speeds due to cost problems and technical difficulties due to the clutch connection stop time (for example, Patent Documents). 1).

JP 2001-130811 A (Pages 6-12, FIG. 2)

  However, in recent years, in order to improve sheet conveyance efficiency, the interval between sheets in the case of conveying a plurality of sheets continuously tends to be short, and while performing continuous sheet conveyance at such a short sheet interval, It is difficult to connect and stop the clutch mechanism in a short time. Further, inconsistency in the conveyance speed at the time of sheet delivery may cause roller surface wear, sheet jamming, or the like, which is not preferable.

  The present invention has been made to solve the above-described problems, and can prevent occurrence of problems caused by inconsistency in the conveyance speed at the time of sheet transfer in the intermediate conveyance roller with a simple apparatus configuration without hindering cost reduction. An object of the present invention is to provide an image forming apparatus that can be suppressed.

To solve the problems described above, an image forming apparatus according to the present invention, an image forming unit for forming an image on a sheet, have row skew correction of the sheet conveyed, the said sheet image at a process speed wherein a resist roller for supplying the forming section, and the resist roller intermediate conveyance rollers for conveying the sheet against the variable speed driving source for driving the intermediate feed roller, the sheet to the new to the intermediate conveyance roller An image is formed on the second surface of the sheet after the image forming unit forms an image on the first surface of the sheet that passes through the registration roller and a conveying roller that supplies at a paper feeding speed faster than the process speed. Therefore, a conveying unit that re-sends the sheet to the intermediate conveying roller at a double-sided conveying speed different from the paper feeding speed faster than the process speed, and the intermediate at the process speed. A driving speed of a driving source of the intermediate conveyance roller is controlled so as to deliver the sheet from a feeding roller to the registration roller, and the sheet is delivered from the conveyance roller to the intermediate conveyance roller at the paper feeding speed. Driving control for controlling the driving speed of the driving source of the intermediate conveying roller and for controlling the driving speed of the driving source of the intermediate conveying roller so as to deliver the sheet from the conveying means to the intermediate conveying roller at the conveying speed at the time of both sides. Part .

  As described above in detail, according to the present invention, it is possible to suppress the occurrence of problems due to the conveyance speed mismatch at the time of sheet transfer in the intermediate conveyance roller with a simple apparatus configuration without hindering cost reduction. An image forming apparatus can be provided.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view showing the overall configuration of an image forming apparatus according to an embodiment of the present invention.

  The image forming apparatus according to the present embodiment includes cassettes 31, 32, 33 and 34 for stacking sheets, pickup rollers 31b, 32b, 33b and 34b for picking up the sheets, and a feed roller for separating and feeding the picked up sheets. 31a, 32a, 33a, 34a and separation rollers 31c, 32c, 33c, 34c, sheet conveying path 35, conveying rollers 36a to 36d that convey the sheet from the sheet conveying path 35 to the intermediate conveying roller 38 (power is transmitted by the clutch). ADU (automatic duplexer) 5, transport rollers 5a to 5d (power is transmitted by a clutch) for transporting sheets in ADU 5, intermediate transport roller 38 driven by a pulse motor, sheet skew correction and timing Registration roller 37 for adjustment and toner A photosensitive drum 20 that forms an image, a fixing unit 24 that fixes the formed toner image on the sheet, a reverse conveyance path 28 through which the sheet on which the toner image is fixed is guided, and the reverse conveyance path 28. Reversing rollers 29 and 30 for switching back the sheet, a CPU 108 and a memory 109 are provided.

  In the image forming apparatus shown in the figure, the following processing is performed. First, the sheets stacked on the cassettes 31, 32, 33 and 34 are picked up by the pickup rollers 31b, 32b, 33b and 34b. The picked-up sheets are separated into sheets one by one by the sheet feeding rollers 31 a, 32 a, 33 a, 34 a and the separation rollers 31 c, 32 c, 33 c, 34 c, and are supplied to the sheet conveyance path 35. The sheet supplied to the sheet conveyance path 35 is conveyed to the front of the intermediate conveyance roller 38 by the conveyance rollers 36a to 36d. The intermediate conveyance roller 38 has a role of guiding a sheet conveyed by the ADU 5 described later and a sheet conveyed in the sheet conveyance path 35 to a registration roller 37 that performs skew correction and timing adjustment of the sheet.

  The sheet guided to the registration roller 37 via the intermediate conveyance roller 38 is subjected to skew correction and timing adjustment, and then the toner image formed on the photosensitive surface of the photosensitive drum 20 is transferred. The toner image transferred to the sheet is fixed on the sheet by the fixing unit 24. The sheet on which the toner image is fixed in this way is discharged out of the machine as it is in single-sided printing, and is guided to the reverse conveyance path 28 when double-sided printing or when the single-sided printed sheet is turned upside down and discharged. .

  When duplex printing is performed, the sheet guided to the reverse conveyance path 28 is switchback conveyed by the reverse rollers 29 and 30 and sent to the ADU 5. The sheet sent to the ADU 5 is transported by the transport rollers 5 a to 5 d and travels again to the intermediate transport roller 38. Thereafter, the image forming process is performed by the photosensitive drum 20 and the fixing unit 24 on the other surface of the sheet conveyed through the ADU 5, thereby realizing double-sided printing on the sheet.

  FIG. 2 is a diagram for explaining sheet conveyance in front of the registration roller, and is an enlarged view of a portion surrounded by a broken line in FIG.

As shown in FIG. 2, in the image forming apparatus having the above-described configuration, when image forming processing is continuously performed on a plurality of sheets (when a plurality of sheets are sequentially conveyed to the registration roller 37), Until the alignment of the preceding sheet P1 by the registration rollers is completed, the succeeding sheet P2 is temporarily held at a predetermined position S before the intermediate conveying roller 38. Similarly, the sheet conveyed to the registration roller again via the ADU 5 is also temporarily held at a predetermined position S _A in the ADU 5 before the intermediate conveyance roller 38.

  FIG. 3 is a functional block diagram for explaining the image forming apparatus according to the present embodiment. The image forming apparatus according to the present embodiment includes a drive control unit 101 and a conveyance speed information acquisition unit 102 in addition to the configurations shown in FIGS. 1 and 2.

  The drive control unit 101 has a role of controlling the driving speed of the intermediate conveyance roller 38 that conveys the sheet to the registration roller 37 that performs skew correction of the conveyed sheet.

  The conveyance speed information acquisition unit 102 has a role of acquiring information related to the conveyance speed of the sheet supplied to the intermediate conveyance roller 38.

  The CPU 108 has a role of performing various processes in the image forming apparatus, and also has a role of realizing various functions by executing a program stored in the memory 109. The memory 109 is composed of, for example, a ROM and a RAM, and has a role of storing various information and programs used in the image forming apparatus.

  Further, the drive control unit 101 moves the intermediate conveyance roller 38 at least three types of speeds different from each other based on information about the conveyance speed acquired by the conveyance speed information acquisition unit 102 (from which route the sheet is conveyed). It is the structure which carries out drive control by.

  FIG. 4 is a timing chart showing the conveyance timing at the time of duplex printing of A4 size sheets and A3 size sheets. In the figure, the upper diagram is a timing chart when switchback conveyance is performed for five A4 sheets (85 PPM (Print Per Minute)), and the lower diagram is when switchback conveyance is performed for five A3 sheets (42 PPM). ) Is a timing chart. In the timing chart of each sheet size, the upper part shows a case where a sheet printed on one side is reversed and discharged, and the lower part shows a case where duplex printing is performed.

  In double-sided printing for A4 size sheets, the first sheet table (1), the second sheet table (2), the third sheet table (3), the first sheet back <1>, the fourth sheet Table (4), second sheet back <2>, fifth sheet front (5), third sheet back <3>, fourth sheet back <4>, fifth sheet back <5> Images are sequentially formed.

  In double-sided printing for A3 size sheets, first sheet table (1), second sheet table (2), first sheet back <1>, third sheet table (3), second sheet Back <2>, 4th sheet back (4), 3rd sheet back <3>, 5th sheet back (5), 4th sheet back <4>, 5th sheet back <5> Images are sequentially formed.

  From the configuration of the image forming apparatus according to the present embodiment and the conveyance speed, the productivity at the time of duplex printing is calculated as follows. FIG. 5 is a diagram for explaining a sheet conveyance path in the image forming apparatus according to the present embodiment. Here, as an example, the sheet conveyance speed and distance as shown in FIG. 5 relating to the conveyance distance and speed are set. In FIG. 5, LP represents the process speed conveyance distance with respect to the process speed region, Lr represents the speed increase reversal conveyance distance (switchback distance) with respect to the speed increase reversal region, and La represents the double-side speed conveyance distance with respect to the double-side conveyance speed region. Represents.

  In order to realize sheet conveyance efficiency (double-sided productivity 100%) equivalent to the case where an image is formed only on one side of a sheet and the paper is reversed and discharged during duplex printing, for example, in the case of 72 PPM and 85 PPM, the following time is used: Thus, the circulation time of the time from the start of the driving of the registration roller 37 to the restart as the paper feeding to the ADU 5 can be expressed by the following equation.

TN5 = 60 / PPM * 5: Circulation time {4.16 sec (72 PPM), 3.53 sec (85 PPM)}
Tat: Total time of double-sided transfer [sec]
= Ta + Tp + Tr + Tra + Tr
PPM: Single-sided productivity (A4 / LT size PPM) 72,85PPM
Vp: Process speed [mm / sec] 340, (410 mm / sec)
Vr: Reversal speed [mm] sec] 800mm / sec
Va: ADU transport speed [mm / sec] 385 mm / sec, (465 mm / sec)
Lp: Process speed transport distance [mm] About 367 mm
Lr: Increased reversal transport distance (switchback distance) [mm] Approximately 296 mm
La: Double-sided speed conveyance distance [mm] Approximately 692mm
Ta: Double-side speed conveyance time [sec] 1797 sec, (1488 sec)
Lpe: Sheet length [mm] 216 mm (LT)
Tpe: Sheet reverse conveyance time [sec] 0.369 sec
Tp: Process speed transfer time [sec] 1.079 sec, (0.895 sec)
Ts: Switchback time (reversal time) [sec] About 0.1 sec
Tra: Resist aligning # time [sec] About 0.07 sec
Tr: Increased speed reverse conveyance time [sec] Approx. 0.27 sec
To: Other time (acceleration / deceleration loss, etc .: 100 msec) About 0.10 sec
() Is transport data at 85 PPM.

  From the above, in the case of a 72 PPM body of 340 mm / sec, the double-sided conveyance total time Tat is 3.79 sec, which is shorter than 4.16 sec of the circulation time TN5 of 5 sheets. Therefore, the treatment with five sheets satisfies the circulation and achieves double-sided productivity of 100%. Similarly, it is 3.29 sec in the 85 PPM body of 410 mm / sec, which is shorter than 3.53 sec of the circulation time TN5 of 5 sheets. From this, it can be seen that both sides satisfy both-side productivity with high efficiency.

  In this embodiment, the relationship between the process speed and the double-sided conveyance speed is set to have a relationship of 1: 1.13, and the CPU 108 changes only two types of motor rotation speeds so that two kinds of speeds can be obtained. The process speed can be realized and the control satisfying 100% duplex productivity can be realized.

  Also, 100% double-sided productivity can be realized by making settings that satisfy the above conditions from the sheet conveyance distance, the sheet conveyance speed, and the printing speed (PPM).

  In addition, if there are restrictions on the sheet interval or reverse conveyance speed at the time of paper supply, it can be dealt with by increasing the conveyance speed at the time of double-sided printing, etc. Also, the paper supply speed, process speed, PPM, double-sided Calculation can be easily selected depending on factors such as the conveyance speed and the reverse conveyance distance.

  In the present embodiment, the drive of the motor driving the fixing unit 24 is distributed, and a clutch mechanism is used for ON / OFF of transmission of driving force. When printing continuously on only one side of the sheet, the clutch is turned off so as not to drive the transport roller in the ADU 5. Further, the speed can be changed by the drive ratio of the input portion from the above fixing driving, and the sheet conveying speed can also be changed by changing the driving to the conveying rollers 36a to 36d after the input.

  The image forming apparatus according to the present embodiment has a configuration in which sheet conveyance control when printing on both sides of a sheet is performed by alternating circulation of one side-both sides-one side-both sides. In the conveyance unit, it is necessary to perform sheet control only once every two sheets with respect to the printing unit. Therefore, the driving of the transport roller in the ADU 5 does not use a lot of pulse motors, but uses clutch driving. Even when the transport roller in the ADU 5 is clutch-driven, the intermediate transport roller 38 is driven by, for example, a pulse motor, and only by changing the drive frequency of the motor, a plurality of transport speeds (for example, process speed, paper feed speed (first speed) 2 types) and double-sided conveyance speed (first speed). Here, an example is given in which the intermediate transport roller is a pair of rollers, but the present invention is not limited to this, and a plurality of roller pairs may be used.

An example of the relationship between process speed: paper feed speed: duplex transport speed is shown below.
At 72 PPM 1: 1.235: 1.13
At 85 PPM 1: 1.122: 1.13

  In this way, by setting the paper feeding speed and the double-sided conveyance speed to a speed (1 to 1.3 times) faster than the process speed, it contributes to noise reduction and stabilization of sheet conveyance control. Can do.

The intermediate transport roller 38 in the present embodiment is, for example,
(1) Feeding speed 420mm / sec
(2) Process speed 340mm / sec
(3) Conveyance speed on both sides 385mm / sec
Thus, three types of sheet conveyance speeds can be realized.

  In this way, by setting the sheet feeding speed to be higher than the process speed, the interval between sheets can be shortened and the number of sheets fed per fixed time can be increased. Also, by setting the ADU 5 duplex conveying speed faster than the process speed, the duplex productivity can be made highly efficient.

  FIG. 6 is a timing chart showing drive timings of conveyance rollers other than the registration roller 37, the intermediate conveyance roller 38, and the intermediate conveyance roller 38 in the image forming apparatus according to the present embodiment.

  The sheet fed from the cassette is transported toward the registration roller 37 by the intermediate transport roller 38 at a paper transport speed of 420 mm / sec. Then, the leading edge of the sheet is abutted against the nip portion of the stopped registration roller 37 and alignment is performed. Thereafter, both the intermediate conveyance roller 38 and the registration roller 37 convey the sheet at a process speed of 340 mm / sec.

  Subsequently, the next sheet that has been temporarily waiting to form an image on one side is conveyed to the registration roller 37 by the intermediate conveyance roller 38 at a sheet feeding conveyance speed of 420 mm / sec.

  The case where the image forming process for one side of the sheet is performed for three sheets (the first sheet is omitted in FIG. 6) will be described. In order to form an image on this surface, the sheet is reversely conveyed, and the sheet is conveyed at an increased speed even after switchback. The speed is slightly reduced in front of the ADU 5, and the sheet is conveyed to the registration roller at an ADU speed of 385 mm / sec. From the figure, it can be seen that at least three types of sheet conveying speeds are realized by the intermediate conveying roller 38.

  In the sheet conveyance timing chart for both sides shown in FIG. 6, the pre-registration SW as a sensor is controlled to trigger the clutch OFF. It is desirable to change according to the set speed and stop time. This is because there is a possibility that the sheet bends between rollers other than the sheet conveyance of a so-called aligning unit that performs skew correction and timing adjustment of the conveyed sheet.

  Next, setting of the sheet conveyance speed will be described. Generally, a clutch mechanism is used for a pickup roller that picks up sheets from the cassettes 31 to 34, and a sheet conveyance loss due to a delay in clutch connection time and a sheet conveyance delay of the pickup rollers 31b to 34b occur. Even when compared with sheet conveyance by the conveyance roller, there are many cases where there is a delay. Such a delay in sheet conveyance time causes a jam or a decrease in copy speed. In such a case, a setting may be made to make a difference between the sheet conveyance and the process speed at the time of printing an image in order to secure a margin regarding the sheet delay and to delay the sheet conveyance.

  However, further increasing the sheet conveyance speed in the apparatus that conveys the sheet at a high speed increases the rubbing noise between the sheet and the guide during sheet conveyance, the driving noise, and the sheet collision noise with the guide during sheet conveyance. It is hard to say that it is preferable. Therefore, the sheet conveying speed is set within a range where the sheet can be stably conveyed.

  Next, speed setting at the time of double-sided conveyance (at the time of sheet conveyance in the ADU 5) will be described. The speed setting for duplex conveyance is often set for each model depending on the model, printing speed (PPM), and the like. If the sheet conveying speed is higher than necessary, there are problems that the temperature of the drive motor and the clutch rises and that the sheet stop control becomes difficult. In addition, a configuration using a large number of pulse motors can perform stable sheet conveyance, but is not preferable in terms of cost.

  When drive control of the transport roller upstream of the intermediate transport roller 38 is realized by using two types of clutches (without having a single ADU transport roller drive motor, drive is transmitted from other fixing drive motors, etc. In this case, the sheet conveyance speed by the conveyance roller needs to be the same as the process speed or change according to the setting by the drive ratio. Even in this case, stable sheet conveyance can be realized by interlocking the sheet conveyance speed of the intermediate conveyance roller 38 with the process speed and the sheet conveyance speed for both sides.

  If the sheet transport speed in the ADU 5 is set to the same speed as the paper feed speed, it is necessary to increase the speed of the ADU 5 more than necessary, and noise during paper feed and conveyance is deteriorated. Noise is reduced by optimal driving.

  In the present embodiment, the sheet feeding / conveying speed necessary for conveying the sheet from the cassette, the process speed for extending the life of the consumables of the photosensitive member and the developer, and the situation where the duplex productivity is high. Situation in which the speed difference between copying and double-sided printing disappears: MAX during alternate circulation: Except for the first and second sheets, and the last two sheets after double-sided printing) Therefore, the above three types of sheet conveying speeds are realized by using only one pulse motor for driving the sheet conveying rollers arranged in front of the registration rollers.

  In this way, by increasing the number of installed pulse motors by one compared to the conventional configuration, the sheet feed stability, the consumable life (or the copy speed can be increased), and double-sided productivity can be achieved. Various types of performance can be satisfied, and the sheet conveying speed can be set freely without setting an unnecessary sheet conveying speed at both sides.

  As described above, in this embodiment, after the toner image is formed on the first surface via the registration roller 37, the drive control unit 101 forms an image on the second surface so as to form an image on the second surface. The first speed when the intermediate transport roller 38 receives a sheet to be retransmitted with respect to the second speed, and the second speed when the intermediate transport roller 38 receives a sheet that is newly supplied to the intermediate transport roller 38 The drive control unit 101 controls the intermediate transport roller 38 so that the first speed is lower than the second speed. I have control. In the present embodiment, the print speed has been described as PPM. However, the same applies to the case of CPM (Copy Per Minute) when performing copy processing.

1 is a cross-sectional view illustrating an overall configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a diagram for explaining sheet conveyance before a registration roller, and is an enlarged view of a portion surrounded by a broken line in FIG. 1. 2 is a functional block diagram for explaining an image forming apparatus according to the present embodiment; FIG. 6 is a timing chart illustrating conveyance timings when duplex printing of A4 size sheets and A3 size sheets is performed. FIG. 6 is a diagram for explaining a sheet conveyance path in the image forming apparatus according to the present embodiment. 4 is a timing chart showing drive timings of conveyance rollers other than the registration roller 37, the intermediate conveyance roller 38, and the intermediate conveyance roller 38 in the image forming apparatus according to the present embodiment.

Explanation of symbols

37 registration rollers, 38 intermediate conveyance rollers, 101 drive control unit, 102 conveyance speed information acquisition unit, 108 CPU, 109 memory.

Claims (3)

An image forming unit for forming an image on a sheet;
There line skew correction of the sheet to be conveyed, and a resist roller for supplying the sheet to the image forming unit at a process speed,
An intermediate conveying roller for conveying the sheet against the resist roller,
A variable speed drive source for driving the intermediate transport roller;
A conveyance roller for newly supplying the sheet to the intermediate conveyance roller at a feeding speed faster than the process speed;
After the image forming unit forms an image on the first surface of the sheet via the registration roller, the sheet is moved from the process speed to the intermediate conveyance roller to form an image on the second surface of the sheet. A conveying means for retransmitting at a speed different from the paper feeding speed at a faster speed on both sides,
The driving speed of the driving source of the intermediate conveyance roller is controlled to transfer the sheet from the intermediate conveyance roller to the registration roller at the process speed, and the conveyance roller to the intermediate conveyance roller at the sheet feeding speed. The drive speed of the drive source of the intermediate conveyance roller is controlled to deliver the sheet, and the drive source of the intermediate conveyance roller is driven to deliver the sheet from the conveyance means to the intermediate conveyance roller at the double-side conveyance speed. An image forming apparatus comprising: a drive control unit that controls a speed ; The image forming apparatus according to claim 1 .
A drive source of the intermediate conveyance roller, the image forming apparatus shall be the pulse motor. The image forming apparatus according to claim 1 or 2,
An image forming apparatus in which power is transmitted by a clutch to a transport roller that supplies a sheet to the intermediate transport roller.

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